1) Field of the Invention
The present invention relates to an optical cross connect unit, optical add-drop multiplexer, light source unit and adding unit suitably employed in the field of wavelength division multiplex transmission where a plurality of different wavelengths are multiplexed for transmission.
2) Description of the Related Art
A wavelength division multiplexing (which will be referred hereinafter to as a WDM) method has been known as a transmission technique which is capable of increasing the transmission capacity and of constructing a network having flexibility in adding and dropping of signals.
This WDM method relates to a technique for multiplexing and transmitting a plurality of different optical wavelength signals, and if multiplexing signals of the same transmission speed, permits the transmission of more information by a quantity corresponding to the number of wavelengths multiplexed as compared with a prior method in which light having one kind of wavelength is modulated and transmitted through one optical fiber. Further, even in the case of low-speed signals, the multiplexing based upon the WDM method can provide a transmission capacity similar to that in a method of sending signals with single wave at a high speed.
On the other hand, since the WDM method is made to make use of the band property of an optical fiber for the purpose of transmitting multiplexed signals (multiple signals), there is a need to set a large wavelength interval whereby the signals undergoes not influence from the adjacent wavelength signals.
Furthermore, on the basis of the above-mentioned WDM transmission system, there has been proposed an optical network in which a repeater, so-called node, is placed in a transmission path on the network. This node has an optical cross connect function to separate wavelength-multiplexed signals in accordance with every wavelength and to distribute the signals to desired transmission paths after conducting wavelength conversion when necessary, and further has an optical ADM function to freely perform the add/drop of desired optical wavelength signals including necessary information.
FIG. 14 is an illustration of a related art. As shown in FIG. 14, the optical cross connect unit 100xe2x80x2 receives wavelength multiplexed signals each having a plurality of different wavelengths xcex1 to xcex8 coming through 16 optical fibers 0xe2x80x2-1 to 0xe2x80x2-16, and performs the conversion of transmission light at every wavelength signal included in each of the wavelength multiplexed signals and the replacement of optical signals such as the interchange among the corresponding transmitting optical fibers 0xe2x80x2-1 to 0xe2x80x2-16.
FIG. 15 is a block diagram showing the related art. As shown in FIG. 15, the optical cross connect unit 100xe2x80x2 is made up of amplifiers 0cxe2x80x2-1 to 0cxe2x80x2-16 for amplifying powers of wavelength multiplexed signals, demultiplexers (branching filters) 10axe2x80x2-1 to 10axe2x80x2-16 for conducting demultplexing in accordance with every wavelength, ORs 21axe2x80x2 for conducting the conversion of a given wavelength signal to an electric signal to transmit the conversion result, OSs 21bxe2x80x2 for newly producing transmission light, 8xc3x9716 DC switches 30axe2x80x2-1 to 30axe2x80x2-16 for taking the charge of control of destinations for 8 optical signals, 16xc3x971 couplers 40axe2x80x2-1 to 40axe2x80x2-16 for multiplexing the optical signals from the 8xc3x9716 DC switches 30axe2x80x2-1 to 30axe2x80x2-16, and amplifiers 0dxe2x80x2-1 to 0dxe2x80x2-16 for amplifying a power of combined light.
Furthermore, FIGS. 16 and 17 are block diagrams each showing the related art. As shown in FIG. 16, each of the ORs 21axe2x80x2 is composed of a photodiode (which will be referred hereinafter to as a PD) 21axe2x80x2-1, while each of the OSs 21bxe2x80x2 is made up of 8 LD light sources 21bxe2x80x2-1, an optical switch 21bxe2x80x2-2 for selecting one of lights (a plurality of light) from the 8 LD light sources 21bxe2x80x2-1, and a modulator 21bxe2x80x2-3 for performing the modulation of light with a given wavelength on the basis of the information converted into an electric signal (photoelectric current) in the PD 21axe2x80x2-1.
On the other hand, the OS 21bxe2x80x2 shown in FIG. 17 comprises a wavelength variable LD 21bxe2x80x2-4 for emitting 8 kinds of light having different wavelengths from each other, and a modulator 21bxe2x80x2-3 for conducting modulation of light with a given wavelength from the wavelength variable LD 21bxe2x80x2-4 on the basis of the information undergoing the electric conversion in the PD 21axe2x80x2-1.
With this arrangement, the prior optical cross connect unit 100xe2x80x2 is made to conduct the cross connect processing for each of the signals included in each of the wavelength multiplexed signals.
In such a mesh-like network, the optical cross connect unit receives N-wave multiplexed signals through M fibers, and separates them in accordance with every wavelength, and conducts a wavelength conversion if necessary, and further performs the optical-wavelength multiplexing for desired signals and transmits them through a desired fiber.
More specifically, an optical signal based upon each of lights wavelength-separated in the demultiplexers 10axe2x80x2-1 to 10axe2x80x2-16 is converted into an electric signal which in turn, is used for modulating light with a wavelength from a new light source, so that desired signals are forwarded toward desired fibers 0xe2x80x2-1 to 0xe2x80x2-16 in a manner that the switching among the paths is made through the switches 30axe2x80x2-1 to 30axe2x80x2-16.
In addition to the aforesaid WDM method of conducting the transmission from point to point, there has been proposed a network based upon a WDM method having an ADM (Add-Drop Multiplexer) function in which a specific-wavelength signal light of the multiplexed signal lights is selectively allowed to pass through a repeating point, so-called node, placed in the middle of the transmission path while the signals with the other wavelengths are received by that node or a different signal light is added therein at this node to be transmitted toward a different node.
FIG. 18 is an illustration of a WDM based network 300xe2x80x2 equipped with an ADM function. Further, FIG. 19 is an illustration of a network 300xe2x80x3 provided with an ADM function. In the illustrations, an ADM unit supplies, in relation to the wavelengths of 5 dropped lights, lights with wavelengths equal to the wavelengths of the 5 (or 4) dropped lights. Incidentally, in the case of actually conducting the branching of P waves to N waves (N: natural number) which is the maximum number in use, the number of wavelengths to be inserted does not always coincide with the P waves.
As shown in FIG. 20, the optical ADM unit 400xe2x80x2-1 includes switches 223xe2x80x2 for selecting one light from 8 LD light sources, amplifiers 223xe2x80x2-1 for amplifying the powers of the lights from the switches 223xe2x80x2, respectively, modulators 227xe2x80x2 for conducting the modulation processing for lights from the switches 223xe2x80x2, respectively, and a multiplexer 228xe2x80x2 for wavelength-multiplexing optical signals from the 5 modulators 227xe2x80x2.
With the above-mentioned arrangement, the optical ADM unit 400xe2x80x2-1 can freely achieve the drop/add of an optical signal.
On the other hand, FIG. 21 illustrates an optical ADM unit 400xe2x80x2-2 equipped with a wavelength variable LD 221xe2x80x2 which outputs 8 kinds of lights having wavelengths different from each other without having 8xc3x975 LD light sources unlike the FIG. 20 optical ADM unit 400xe2x80x2-1. Even the optical ADM unit 400xe2x80x2-2 shown in FIG. 21 is also capable of freely conducting the drop/add in a state where the signal is in an optical condition as well as the optical ADM unit 400xe2x80x2-1.
There is a problem which arises with the related optical cross connect unit 100xe2x80x2, however, in that the equipment of 16xc3x978xc3x978 LD light sources becomes necessary and the management of the light sources themselves becomes troublesome. In addition, difficulty is encountered to dynamically switch the wavelengths according to the circumstances and the transmission is made with predetermined wavelengths, with the result that its system lacks flexibility.
Furthermore, similarly, the optical ADM 400xe2x80x2-1 is required to be equipped with 8xc3x975 LD light sources, with the result that the management of the light sources themselves becomes troublesome.
Although a reductancy arrangement such as the preparation of spare light sources for provision against the breakdown of light sources should be taken into consideration for the real system, the preparation of spare light sources for all the light sources in the wavelength multiplexing and transmitting section heavily sacrifices cost, and if spare light sources for all the light sources are prepared even in the case of the equipment of a large number of wavelength multiplexing systems, the cost of the light source section extremely increases.
Still further, although the arrangement can also be made with wavelength variable light sources, this case can create a problem in the sweep time taken until setting to a desired wavelength and the influence on the other signals in the meantime.
The present invention has been developed with a view to eliminating these problems, and it is therefore an object of this invention to provide an optical cross connect unit, optical add-drop multiplexer, light source unit and adding unit which are capable of, when many light sources are necessary for conducting the modulation processing through a modulator or the like, employing given optical wavelengths from a small number of light sources for much modulation processing.
For this purpose, in accordance with the present invention, there is provided an optical cross connect unit comprising M wavelength separating sections for receiving multiplexed optical signals each having N kinds of wavelengths different from each other through M optical fibers, respectively, and for wavelength-separating each of the multiplexed optical signals into N optical signals, M optical reproduction relay (repeating) sections each for conducting an optical reproduction and relay in a manner of making a conversion of each of the N optical signals, wavelength-separated in each of the wavelength separating sections, into an electric signal and then modulating it with a desired optical wavelength, a refill section for mutually refilling M sets of optical signals optically reproduced and relayed in the optical reproduction relay sections, a focusing section for focusing the M sets of optical signals refilled in the refill section, and a light source unit for supplying input lights having desired wavelengths to be modulated in the M optical reproduction relay sections.
In this optical cross connect unit, the light source unit includes N light sources for outputting lights having the aforesaid N kinds of optical wavelengths, a multiplexing and branching section for multiplexing the lights from the N light sources to produce a multiplexed light having N kinds of optical wavelength components and further for branching the multiplexed light into Mxc3x97N lights to output them as multiplexed and distributed lights, M wavelength filter sections for distributively receiving N multiplexed and distributed lights of the Mxc3x97N multiplexed and distributed lights branched in the multiplexing and branching section to output N lights due to the passage of only arbitrary wavelengths of the aforesaid N kinds of optical wavelengths, and a wavelength setting control section for setting optical wavelengths, which pass through the wavelength filter sections, so that they differ from each other, with the N lights from each of the M wavelength filter sections being supplied as the aforesaid input lights.
Accordingly, the optical cross connect unit according to this invention can generate a large number of wavelength multiplexed signals from one set of light sources, with the result that the control/management of the light source wavelengths are expectable to be facilitated and the wavelength selection can arbitrarily be made through the wavelength filter sections, which enhances the extension of the optical cross connect unit itself and increases the number of lights to be distributed at a low cost.
Furthermore, an optical add-drop multiplexer according to this invention is composed of a dropping section for dropping an optical signal with arbitrary P kinds of wavelengths of N kinds of different wavelengths constituting a multiplexed optical signal having the N kinds of wavelengths to be transmitted through a transmission optical fiber, and an adding section for adding a transmission optical signal having Pxe2x80x2 kinds of wavelengths corresponding to the wavelengths demultiplexed in the demultiplexing section into the transmission optical fiber. The adding section is composed of N light sources for outputting lights with N kinds of optical wavelengths, a multiplexing and branching section for multiplexing the lights from the N light sources to produce a multiplexed light having N kinds of optical wavelength components and further for branching the multiplexed light into Mxc3x97N lights to output them as multiplexed and distributed lights, M wavelength filter sections for distributively receiving N multiplexed and distributed lights of the Mxc3x97N multiplexed and distributed lights branched in the multiplexing and branching section to output N lights due to the passage of only arbitrary wavelengths of the aforesaid N kinds of optical wavelengths, a wavelength setting control section for setting optical wavelengths, which pass through each of the wavelength filter sections, so that they differ from each other, and a modulating section for receiving N lights from any one of the M wavelength filter sections as input lights to perform data modulation processing for the input lights, with the N lights from each of the wavelength filter sections of the inserting section, other than the aforesaid one wavelength filter section, being used as input lights to be taken when conducting the data modulation processing in an adding section of another optical add-drop multiplexer coupled through the aforesaid transmission optical fiber.
Thus, since the optical add-drop multiplexer according to this invention is composed of a dropping section for dropping an optical signal with arbitrary P kinds of wavelengths of N kinds of different wavelengths constituting a multiplexed optical signal having the N kinds of wavelengths to be transmitted through a transmission optical fiber, and an adding section for adding a transmission optical signal having Pxe2x80x2 kinds of wavelengths corresponding to the wavelengths dropped in the dropping section to the transmission optical fiber. The adding section is composed of N light sources for outputting lights with N kinds of optical wavelengths, a multiplexing and branching section for multiplexing the lights from the N light sources to produce a multiplexed light having N kinds of optical wavelength components and further for branching the multiplexed light into Mxc3x97N lights to output them as multiplexed and distributed lights, M wavelength filter sections for distributively receiving N multiplexed and distributed lights of the Mxc3x97N multiplexed and distributed lights branched in the multiplexing and branching section to output N lights due to the passage of only arbitrary wavelengths of the N kinds of optical wavelengths, a wavelength setting control section for setting optical wavelengths passing through each of the wavelength filter sections so that they differ from each other, and a modulating section for receiving N lights from one set of wavelength filter sections of the M wavelength filter sections as input lights to perform data modulation processing for the input lights while the N lights from each of the wavelength filter sections of the adding section other than the one set of wavelength filter sections are used as input lights to be taken when conducting the data modulation processing in an adding section of another optical add-drop multiplexer coupled through the transmission optical fiber, the wavelength filter sections can arbitrarily select lights with the same wavelengths as those of the dropped lights through the use of a wavelength multiplexed signal distributing light source.
Moreover, a light source unit for supplying input lights having desired wavelengths according to this invention comprises N light sources for outputting lights with N kinds of optical wavelengths, a multiplexing and branching section for multiplexing the lights from the N light sources to produce a multiplexed light having N kinds of optical wavelength components and further for branching the multiplexed signal into at least N lights to output them as multiplexed and distributed lights, N wavelength filters for receiving the N multiplexed and distributed lights branched in the multiplexing and branching section but for allowing the passage of only one optical wavelength of the N kinds of optical wavelengths, and a wavelength setting control section for setting the optical wavelengths to be allowed to pass through the N wavelength filters so that, when arbitrarily combined, they are different from each other.
Accordingly, since a light source unit for supplying input lights having desired wavelengths according to this invention comprises N light sources for outputting lights with N kinds of optical wavelengths, a multiplexing and branching section for multiplexing the lights from the N light sources to produce a multiplexed light having N kinds of optical wavelength components and further for branching the multiplexed signal into at least N lights to output them as multiplexed and distributed lights, N wavelength filters for receiving the N multiplexed and distributed lights branched in the multiplexing and branching section but for allowing the passage of only one optical wavelength of the N kinds of optical wavelengths, and a wavelength setting control section for setting the optical wavelengths to be allowed to pass through the N wavelength filters so that, when arbitrarily combined, they are different from each other, the wavelength filters can select lights with desired wavelengths, so that the light source unit can preferably be used as light source means as compared with a type of electrically switching the wavelengths.
Furthermore, a light source unit according to this invention comprises N light sources for outputting lights having N kinds of optical wavelengths, a multiplexing and branching section for multiplexing the lights from the N light sources to produce a multiplexed light having N kinds of optical wavelength components and further for branching the multiplexed light into M lights to output them as multiplexed and distributed lights, M wavelength filter sections for distributively receiving M multiplexed and distributed lights to output M lights each of which wavelengths correspond to one of the N kinds of optical wavelengths, and a wavelength setting control section for setting optical wavelengths, which pass through the wavelength filter sections.
Accordingly, the light source unit according to this invention can generate a large number of wavelength multiplexed signals from one set of light sources, with the result that the control/management of the light source wavelengths are expectable to be facilitated and the wavelength selection can arbitrarily be made through the wavelength filter sections, which increases the number of lights to be distributed at a low cost.
Still further, an adding unit according to this invention comprises N light sources for outputting lights with N kinds of optical wavelengths, a multiplexing and branching section for multiplexing said lights from the N light sources to produce a multiplexed light having N kinds of optical wavelength components and further for branching the multiplexed light into M lights to output them as multiplexed and distributed lights, M wavelength filter sections for distributively receiving M multiplexed and distributed lights to output M lights each of which wavelengths correspond to one of the N kinds of optical wavelengths, a wavelength setting control section for setting optical wavelengths, which pass through the wavelength filter sections, and a modulating section for receiving M lights from the M wavelength filter sections as input lights to perform data modulation processing for the input lights.
Accordingly, for instance, the light corresponding to the light dropped in an optical add-drop multiplexer can be supplied as add light.
Moreover, a light source unit for supplying input lights according to this invention comprises N light sources for outputting lights with N kinds of optical wavelengths, a multiplexing and branching section for multiplexing the lights from said N light sources to produce a multiplexed light having N kinds of optical wavelength components and further for branching the multiplexed light into M lights to output them as multiplexed and distributed lights, M wavelength filters for receiving the M multiplexed and distributed lights branched in the multiplexing and branching section, and for allowing the passage of only one optical wavelength of the N kinds of optical wavelengths; and a wavelength setting control section for setting the optical wavelengths to be allowed to pass through the N wavelength filters.
Accordingly, the wavelength filters can select lights with desired wavelengths, so that the light source unit can preferably be used as light source means as compared with a type of electrically switching the wavelengths.